For most UK small businesses already on Microsoft 365 Business Premium, Teams Phone is the simpler pick — one licence, one login, one vendor, from about £9/user/month for the Teams Phone Standard add-on plus a call plan. 3CX wins on price for very small teams (under 15 users) and on call-centre features like advanced queues, call recording as standard, and granular IVR. Pick Teams Phone if you want one stack; pick 3CX if you want phone-first features at a lower per-user price.
What each platform actually is
Microsoft Teams Phone is Microsoft's PBX replacement built into Teams. You buy a Teams Phone licence, add a call plan (or bring your own SIP trunk via Direct Routing or Operator Connect), and your staff make and take calls from the Teams app they already use. It replaces your PBX, not your chat tool.
3CX is a self-hosted or vendor-hosted PBX that has been around since 2005. The Free tier supports up to 10 users; paid tiers add call recording, call queues, CRM integration and more. 3CX has a Teams integration but is a separate product and separate app.
Price at real SME scale
Here's how it lands for a 20-user UK business in 2026:
- Teams Phone: £9/user/month for Teams Phone Standard + ~£9/user/month for a Business Voice plan = £18/user/month. Handsets £80–£200 one-off. No hosting, no PBX to maintain.
- 3CX Pro (hosted, 20 simultaneous calls): around £250–£350/month for the system plus SIP trunk (~£3/channel/month + pennies per minute) + handsets. Works out roughly £15–£20/user/month depending on call volume.
At 5 users, 3CX is substantially cheaper. At 50 users, Teams Phone is comparable and often cheaper once you account for PBX admin time. Above 100, it depends entirely on feature needs.
Features where Teams Phone wins
- Single pane of glass. Calls, chat, meetings, files, presence — all in Teams. Staff don't learn a new app.
- Device management. Intune-managed mobiles automatically get the right Teams Phone policies.
- Compliance recording. Microsoft-certified partners like CallCabinet plug in natively.
- No PBX to patch. Microsoft runs it. You don't.
Features where 3CX wins
- Call-centre depth. Advanced queues, skills-based routing, wallboards and supervisor intrusion are built in, not add-ons.
- Call recording as standard. Included on every paid tier, no extra licence needed.
- IVR without PhD. The drag-and-drop call-flow editor is genuinely simpler than Teams Phone auto-attendants.
- SIP device freedom. Works with almost any SIP handset — Yealink, Snom, Fanvil, Grandstream — at a wider price range.
Call quality and reliability
Both are fine on a decent connection. Teams Phone uses Microsoft's global backbone and is very stable. 3CX quality depends on your SIP trunk provider — pick a tier-1 UK provider (Gamma, Voiceflex, TelcoSwitch) and it's indistinguishable from Teams. What matters more for both: your office WiFi and broadband. Cheap consumer gear is the number one cause of "the phones sound bad" tickets. If yours isn't up to it, proper commercial WiFi and a business-grade circuit fix it faster than changing PBX.
PSTN switch-off — both are ready
The UK PSTN switch-off completes on 31 January 2027. Stop-sell is already in place in most exchanges. Both Teams Phone and 3CX are cloud/IP-based and unaffected — the thing that needs to move is whatever ISDN or analogue line feeds your current PBX. If you're still on BT ISDN, you need to pick a successor now.
When we recommend which
- Pick Teams Phone if you're already on Microsoft 365 Business Premium, your staff live in Teams, and you want one vendor.
- Pick 3CX if you're under 15 users on a tight budget, you run a small contact centre, or you need recording on every call at no extra cost.
- Pick neither if you're happy with your current system and it's already IP-based; don't switch for the sake of it.
For most of our West Sussex clients we've landed on Teams Phone with Operator Connect via a UK carrier. It keeps the vendor count low and the admin overhead close to zero. For a minority — typically solicitors with conveyancing queues or clinics with appointment hotlines — 3CX is the better fit.
How Syntek handles the move
Whichever you pick, we do the dull parts: number porting, call-flow design, handset supply, training, and the test-call script on cutover day. Most moves take 3–5 weeks from signed quote to go-live. See our telephony service or book a call on .
FAQ
Is Teams Phone cheaper than 3CX?
For fewer than 15 users, 3CX is usually cheaper. Above 20 users, Teams Phone with a Business Voice plan is typically comparable once you factor in handsets, hosting and call plans.
Can I keep my existing phone numbers?
Yes. Both platforms support number porting from any UK provider. Porting takes 5–10 working days and needs a letter of authority from the account holder.
Does 3CX work well with Microsoft 365?
It integrates through Microsoft 365 contacts and calendar presence, and has a Teams integration. It does not replace Teams internal chat — it sits alongside it.
What happens to my phone system after the PSTN switch-off?
Both Teams Phone and 3CX are cloud-based and unaffected by the 31 January 2027 PSTN switch-off. Only legacy ISDN and analogue lines need to move.